Signaling method for scaling parameter in chroma from luma intra prediction mode

Abstract

Methods and apparatuses for performing cross-component intra prediction, including: receiving a current chroma block from a coded bitstream; determining, from the coded bitstream, that a scaling factor used for the current chroma block in a chroma for luma (CfL) intra prediction mode; deriving a predicted scaling factor based on first neighboring samples of the current chroma block and second neighboring samples of a luma block that is co-located with the current chroma block; using the predicted scaling factor as the scaling factor used for the current chroma block in the CfL intra prediction mode; reconstructing the current chroma block after scaling the current chroma block based on the predicted scaling factor.

What is claimed is: 
     
         1 . A method for performing cross-component intra prediction, the method being performed by at least one processor and comprising:
 receiving a current chroma block from a coded bitstream;   determining, from the coded bitstream, that a scaling factor used for the current chroma block in a chroma from luma (CfL) intra prediction mode;   deriving a predicted scaling factor based on first neighboring samples of the current chroma block and second neighboring samples of a luma block that is co-located with the current chroma block;   using the predicted scaling factor as the scaling factor used for the current chroma block in the CfL intra prediction mode;   reconstructing the current chroma block after scaling the current chroma block based on the predicted scaling factor,   wherein the CfL intra predication mode comprises a sum of (i) a product of the scaling factor with an alternating current (AC) contribution of a luma block, the AC contribution determined in accordance with a difference between reconstructed luma samples subsampled into a chroma resolution and an average of the reconstructed luma samples subsampled into the chroma resolution and (ii) a direct current (DC) contribution of the current chroma block determined in accordance with an intra DC mode, and   wherein the predicted scaling factor is derived based on: (i) a row of chroma samples located above the current chroma block, (ii) a row to a left of the current chroma block, (iii) a plurality of rows of luma samples above a co-located luma block, and (iv) a plurality of rows of luma samples to the left of the co-located luma block,   wherein the plurality of rows of luma samples above the co-located luma block and the plurality of rows of luma samples to the left of the co-located luma block are down sampled before deriving the predicted scaling factor based on determining a YUV format of the current chroma block is no YUV444,   wherein the predicted scaling factor is included in a plurality of scaling factors,   wherein a scaling parameter is used to reorder the plurality of scaling factors, and   wherein an index is used to select the predicted scaling factor from among the plurality of scaling factors,   wherein when the predicted scaling factor is greater than 0, an available sign is reordered as positive (+1), zero (0), and negative (−1),   wherein when the predicted scaling factor is equal to zero, the available sign is reordered as zero (0), positive (+1), and negative (−1), and   wherein when the predicted scaling factor is less than zero, the available sign is reordered as negative (−1), zero (0), and positive (1).   
     
     
         2 . The method of  claim 1 , wherein the predicted scaling factor is derived using a least mean square calculation. 
     
     
         3 . The method of  claim 1 , wherein the predicted scaling factor is derived separately for a first chroma component and a second chroma component. 
     
     
         4 . The method of  claim 1 , wherein the predicted scaling factor is included in a plurality of scaling factors, and
 wherein a scaling parameter is used to reorder at least one from among an available sign value for the plurality of scaling factors, and an absolute magnitude corresponding to the scaling factor.   
     
     
         5 . The method of  claim 1 , wherein based on a flag indicating that the scaling factor is not 0, a scaling parameter is used to reorder a plurality of scaling factors except for 0, and
 wherein the predicted scaling factor is selected from among the plurality of scaling factors.   
     
     
         6 . The method of  claim 1 , wherein a scaling parameter is used to select a subset of scaling factors from among a plurality of scaling factors, and
 wherein the predicted scaling factor is selected from among the subset of scaling factors based on a syntax element signaled in the coded bitstream.   
     
     
         7 . A device for performing cross-component intra prediction, the device comprising:
 at least one memory configured to store program code; and   at least one processor configured to access the program code and operate as instructed by the program code, the program code including:
 receiving code configured to cause the at least one processor to receive a current chroma block from a coded bitstream; 
 determining code configured to cause the at least one processor to determine, from the coded bitstream, a scaling factor used for the current chroma block in a chroma for luma (CfL) intra prediction mode; 
 deriving code configured to cause the at least one processor to derive a predicted scaling factor based on first neighboring samples of the current chroma block and second neighboring samples of a luma block that is co-located with the current chroma block; 
 using code configured to cause the at least one processor to use the predicted scaling factor as the scaling factor used for the current chroma block in the CfL intra prediction mode; and 
 reconstructing code configured to cause the at least one processor to reconstruct the current chroma block after scaling the current chroma block based on the predicted scaling factor, 
 wherein the CfL intra predication mode comprises a sum of (i) a product of the scaling factor with an alternating current (AC) contribution of a luma block, the AC contribution determined in accordance with a difference between reconstructed luma samples subsampled into a chroma resolution and an average of the reconstructed luma samples subsampled into the chroma resolution and (ii) a direct current (DC) contribution of the current chroma block determined in accordance with an intra DC mode, and 
 wherein the predicted scaling factor is derived based on: (i) a row of chroma samples located above the current chroma block, (ii) a row to a left of the current chroma block, (iii) a plurality of rows of luma samples above a co-located luma block, and (iv) a plurality of rows of luma samples to the left of the co-located luma block, 
 wherein the predicted scaling factor is included in a plurality of scaling factors, 
 wherein a scaling parameter is used to reorder the plurality of scaling factors, and 
 wherein an index is used to select the predicted scaling factor from among the plurality of scaling factors, 
 wherein when the predicted scaling factor is greater than  0 , an available sign is reordered as positive (+1), zero (0), and negative (−1), 
 wherein when the predicted scaling factor is equal to zero, the available sign is reordered as zero (0), positive (+1), and negative (−1), and 
 wherein when the predicted scaling factor is less than zero, the available sign is reordered as negative (−1), zero (0), and positive (1). 
   
     
     
         8 . The device of  claim 7 , wherein the predicted scaling factor is derived using a least mean square calculation. 
     
     
         9 . The device of  claim 7 , wherein the predicted scaling factor is derived separately for a first chroma component and a second chroma component. 
     
     
         10 . The device of  claim 7 , wherein the predicted scaling factor is included in a plurality of scaling factors, and
 wherein a scaling parameter is used to reorder at least one from among an available sign value for the plurality of scaling factors, and an absolute magnitude corresponding to the scaling factor.   
     
     
         11 . The device of  claim 7 , wherein based on a flag indicating that the scaling factor is not 0, a scaling parameter is used to reorder a plurality of scaling factors except for 0, and
 wherein the predicted scaling factor is selected from among the plurality of scaling factors.   
     
     
         12 . The device of  claim 7 , wherein the predicted scaling factor is included in a plurality of scaling factors,
 wherein a scaling parameter is used to reorder the plurality of scaling factors, and   wherein an index is used to select the predicted scaling factor from among the plurality of scaling factors.   
     
     
         13 . A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by one or more processors of a device for performing cross-component intra prediction, cause the one or more processors to:
 receive a current chroma block from a coded bitstream;   determine, from the coded bitstream, that a scaling factor used for the current chroma block in a chroma for luma (CfL) intra prediction mode;   derive a predicted scaling factor based on first neighboring samples of the current chroma block and second neighboring samples of a luma block that is co-located with the current chroma block;   use the predicted scaling factor as the scaling factor used for the current chroma block in the CfL intra prediction mode; and   reconstruct the current chroma block after scaling the current chroma block based on the predicted scaling factor,   wherein the CfL intra predication mode comprises a sum of (i) a product of the scaling factor with an alternating current (AC) contribution of a luma block, the AC contribution determined in accordance with a difference between reconstructed luma samples subsampled into a chroma resolution and an average from the reconstructed luma samples subsampled into the chroma resolution and (ii) a direct current (DC) contribution of the current chroma block determined in accordance with an intra DC mode, and   wherein the predicted scaling factor is derived based on: (i) a row of chroma samples located above the current chroma block, (ii) a row to a left of the current chroma block, (iii) a plurality of rows of luma samples above a co-located luma block, and (iv) a plurality of rows of luma samples to the left of the co-located luma block,   wherein the predicted scaling factor is included in a plurality of scaling factors,   wherein a scaling parameter is used to reorder the plurality of scaling factors, and   wherein an index is used to select the predicted scaling factor from among the plurality of scaling factors,   wherein when the predicted scaling factor is greater than 0, an available sign is reordered as positive (+1), zero (0), and negative (−1),   wherein when the predicted scaling factor is equal to zero, the available sign is reordered as zero (0), positive (+1), and negative (−1), and   wherein when the predicted scaling factor is less than zero, the available sign is reordered as negative (−1), zero (0), and positive (1).   
     
     
         14 . The non-transitory computer-readable medium of  claim 13 , wherein the predicted scaling factor is derived using a least mean square calculation. 
     
     
         15 . The non-transitory computer-readable medium of  claim 13 , wherein the predicted scaling factor is derived separately for a first chroma component and a second chroma component.